Prior tubular type reactors disclosed in "Polymerization of Ethylene and Propylene to Amorphous Copolymers with Catalyst of Vanadium Oxychloride and Alkylaluminumhalides"; E. Junghanns, A Gumboldt and Gdier, Marcomolecular Chemistry Vol. 58 Dec. 12, 1962 p. 18-42 show the use of a tubular reactor to produce ethylene propylene copolymer in which the compositions vary along the chain length. Specifically, a Ziegler catalyst (vanadium compound and aluminum alkyl) is used in a tubular reactor to produce amorphous ethylene propylene copolymer. It is further disclosed that at the beginning of the tube, ethylene is preferentially polymerized and no additional ethylene monomer mixture is added during polymerization, thus the concentrations of the monomers change in favor of the propylene along the tube. These changes in concentration take place during chain propagation such that copolymer chains are produced which contain more ethylene at one end than at the other end. It is also disclosed that copolymers made in the tube reactor are chemically non-uniform, but fairly uniform with regard to molecular weight distribution.
Another tubular reactor process is disclosed in "Laminar Flow Polymerization of EPDM Polymer" by J. F. Wehner: ACS Symposium Series 65 (1978) p. 140-152. Wehner discloses the results of a computer simulation undertaken to determine the effect of tubular reactor solution process with Ziegler catalyst on molecular weight distribution of the polymer product. The specific polymer simulated was an elastomeric terpolymer of ethylene/propylene/1-4 hexadiene. It is particularly stated that since the monomers have different reactivities, polymer of varying composition will be obtained as the monomers are depleted. However, whether the composition varies intra or intermolecularly is not disclosed.
U.S. Pat. No. 3,681,306 to Wehner discloses a process for producing ethylene/higher-alpha-olefin copolymers having good processability by polymerizing in at least two consecutive reactor stages. According to Wehner this two stage process provides a simple polymerization process that permits tailor making ethylene alpha-olefin copolymers having predetermined properties, particularly those contributing to processability in commercial applications such as cold flow, high green strength and millability. The disclosed preferred process is one tubular reactor followed by one pot reactor. However, Wehner also discloses that one tubular reactor could be used but operated in different reaction conditions to simulate two stages.
U.S. Pat. No. 3,625,658 to Closen discloses a closed circuit tubular reactor apparatus with high recirculation rates of reactants which can be used to make elastomers of ethylene and propylene.
U.S. Pat. No. 4,065,520 to Bailey et at. discloses the use of a batch reactor to make ethylene copolymers, including elastomers, having a broad compositional distribution. Several feed tanks for the reactor are arranged in series with the feed to each being varied to make the desired polymer. The products made have crystalline and semi-crystalline to amorphous regions and gradient changes in between. The catalysts used were vanadium compounds alone or in combination with titanium compounds and were exemplified by vanadium oxytrichloride and diisobutyl aluminum chloride. In all the examples titanium compounds are used. The polymer chains produced have a compositionally dispersed first length and uniform second length.
British Patent No. 1,233,599 is illustrative of a two stage polymerization process typically used to produce polymers of polymodal molecular weight distribution. While copolymers of ethylene are disclosed, the examples and disclosure are directed towards polyethylene homopolymers and crystalline copolymers e.g. 95% ethylene.
U.S. Pat. No. 4,078,133 discloses an ethylene propylene rubber composition having a bimodal distribution prepared by carrying out the polymerization in two separate reactors connected in series.
U.S. Pat. No. 3,681,306 discloses a two stage polymerization process for the preparation of ethylene/propylene co and terpolymers. In one embodiment the first stage is a pipe reactor and the second stage is a back mix pot reactor. The polymerization is carried out so that the average ethylene to alpha-olefin ratio in one stage is at least 1.3 times the average of another stage.
U.S. Pat. No. 4,786,697 to Cozewith et at. discloses a polymodal molecular weight distribution ethylene copolymer comprising at least two modes of differing molecular weight produced utilizing at least two catalyst species in a tubular plug flow reactor. In particular, the Cozewith process is carried out in a mixed free reactor system which is defined to be one in which substantially no mixing occurs between portions of the reactor mixture that contain polymer chains initiated at different times. In addition, the product can be removed at one or more locations. This process produces polymer of a polymodal molecular weight distribution. Alternately, two or more catalysts with different propagation rates can be used. Suitable reactors are disclosed to be continuous flow tubular or stirred batch reactors and multiple monomer feeds and residence times as low as 1 second are also disclosed.